That's not true. I was on a 'training course' regarding the industry markets and asked the question of the experts. The industry/watchdog have decided that the Supplier shall be the single point of contact to customers. No DNO information should be provided on the bill.Dial the emergency number for your DNO, your DNO not your supplier. If you do not know the number it WILL be on your bill
It's all to avoid confusion apparently. When you call the said supplier they are of course trained and competent to direct your call to the appropriate DNO for your area.